This invention relates to printable pressure-sensitive adhesive tape, a preferred embodiment relating to packaging tapes which have aggressive, high performance adhesives.
A standard item of commerce for many years have been a family of printable pressure-sensitive adhesive tapes. The backing of such tapes must, of course, be receptive to flexographic ink or other printing inks; if the nature of the backing is such that it does not inherently possess ink-receptivity, it is necessary to provide some type of coating which imparts that characteristic. Printable tapes have, however, always embodied a compromise. For example, after a tape is printed, it is typically wound convolutely upon itself in roll form, subsequently unwound and cut to the desired length when it is to be used. If the adhesive is extremely aggressive, it tends to remove all or part of the printed indicia from the back during the unwinding process. Although the transfer of such indicia can be eliminated, or at least inhibited, by the application of a low-adhesion backsize following the printing operation, this necessitates an extra step and increases the cost of the product. Hence, where the tape is to be printed, adhesives having low to moderate adhesion are usually employed.
Others have previously attempted to solve the problem of obtaining a backsize coating which has the combined characteristics of adhesion to the backing, ink retention and good unwind characteristics. In this regard, see Canadian Pat. No. 772,120, which discloses the use of acrylate and methacrylate polymers and copolymers as a backsize. Attention is also directed to German Offenlegungsschrift No. 2,018,929, which describes modifying the backsize of the Canadian patent by blending with it a vinylidene chloride: acrylonitrile copolymer. Each of these two backsizes is useful to a degree, but neither functions effectively when the face side of the tape is provided with a strongly aggressive pressure-sensitive adhesive. When such an adhesive is employed (as is commonly the case with packaging tapes), unwinding a printed roll or tape results in (1) removing an unacceptable amount of the printed indicia and/or (2) an unacceptably high unwind force.